The present invention relates to a bacteriological investigation method particularly intended for the microbiological analysis of liquid mediums.
This method may be applied generally to the identification of one or more bacteria in a liquid medium. The following bacterial species may be mentioned by way of example: Escherichia coli, Klebsiella, Citrobacter, Enterobacter, Aeromonas, Pseudomonas aeruginosa, Staphylococcus, Streptococcus and Bacillus.
The method has been used by the inventors, in the premises of the Pasteur Institute in LILLE, for the bacteriological testing of water.
The bacteriological investigation method developed by Pasteur more than a century ago is presently in current use, since its exactness and efficiency are well established.
However, the applications of this method are limited: in fact, it always makes use of solely manual techniques and the times required for analysis are considerable. Microbiological analyses firstly require the making of selective or non-selective cultures of the germs to be identified, then a stage for the isolation of the various bacterial species present, since identification generally proceeds from a "pure culture". The identification of bacterial species is therefore possible; it requires a frequently high number of biochemical tests.
This well known method always uses manual techniques requiring the intervention of a technician at all stages. It is divided into several stages and uses a large number of culture mediums for isolating and identifying a bacterial species. The response times are of the order of 24 hours to 3 days depending on whether the test is negative or positive.
It has therefore become indispensable to develop a method of bacteriological investigation using an automated method whose response time would be reduced considerably and whose cost price would be much lower.
If it has seemed necessary to automate biological investigation, it has also become indispensable to develop a method which may be carried out continuously. In fact, it is quite useless to improve the sensitivity of known manual methods for samples which are in no way representative. This is particularly the case when one analyses a sample of several milliliters of water taken from a river or pipe which frequently contains several thousands of cubic meters.
The main idea of the method according to the invention has been to link the taking of samples and the analysis to make the method completely automatic and to enable it to be carried out continuously.
Continuous automatic analysers are currently known, which are used for example in the chemical field or in the analysis of blood, which analysers suck in the samples from a pipe through the intermediary of a pump, whilst dividing the latter into segments by means of a gas or liquid. It has not been possible for these apparatus to be applied directly to microbiological analysis and the inventors have come up against the main drawback inherent in the type of sample used and even in the apparatus, namely that of rinsing. In fact, the problem of the separation of samples, common to all chemical analyses and conditioning the speed of sampling has become more precisely in this case, a problem of decontamination made more complex by two main reasons:
-- firstly, the unusual length of the circuit and the time taken by the samples to pass through this circuit have nothing in common with those of chemical circuits and favour greater progressive contamination.
-- then, the circuit envisaged in this case is a living circuit which may thus be subject to perpetual evolution: in chemical circuits, a molecule or atom passing from one sample to another, remains as it is in the contaminated sample; on the contrary, in a bacteriological circuit, if a bacterium passes from one sample to the next, it multiplies rapidly in the latter.